<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 100px;
            height: 100px;
            background-color: lightblue;
        }
    </style>
</head>
<body>
    <div id='div'>
        <button id='btn'>
            +1
        </button>
    </div>
    <script>
        const divEl = document.querySelector('#div')
        const btnEl = document.querySelector('#btn')
        divEl.addEventListener('click', (event) => {
            console.log('===')
        }, {capture: true})
        
    </script>
    <script src='./arr-to-tree.js'></script>
</body>
</html>